I'm unable to Merge my rooms to three which wouldn't be that bad, I'd just restart the vault, but I bought 40 lunchboxes and don't want to have wasted the money. Any fixes minus restarting?

Hi

Did you double check to make sure all of the rooms are upgraded to the same level? For instance, if you have upgraded a Cafeteria twice, the room next door won't merge until you upgrade it twice.

Pro tip: You save caps if you make a larger room first and then upgrade.